Spectrogram default color map

I noticed that the spectrogram has "jet" hardcoded as default colormap. Jet is really not a good choice in my opinion since it isn't perceptually uniform. I will set "viridis" as default on our end.

I think..

• jet should not be the default, or..
• if jet stays default, it would be good to be able to set a different default in the .env file, without having to patch the code base